A fin-and-tube heat exchanger has been known that includes a plurality of plate-like fins arranged with predetermined fin pitches, and a plurality of heat transfer tubes each having a flat shape. In the heat exchanger, the cross section of the heat transfer tube is formed into a substantially elliptical shape or a substantially oval shape. A plurality of cutout portions extending from one side portion of the fin toward the other side portion of the fin are formed in the fin. The plurality of heat transfer tubes are inserted into the plurality of cutout portions of the fin and extend in a direction in which the plurality of fins are arranged. Note that the ends of each heat transfer tube are connected to distribution pipes or headers that form a refrigerant passage with the heat transfer tubes. Further, the heat exchanger exchanges heat between a fluid that causes heat exchange, such as air flowing between the fins, and a fluid subjected to heat exchange, such as water and refrigerant flowing through the heat transfer tubes.
Further, in the heat exchanger, fin collars that are vertically cut and raised from the peripheral edges of the cutout portions are formed on the fin. The heat transfer tubes inserted into the cutout portions and the fin collars are bonded to each other by furnace brazing or with an adhesive, thereby improving the degree of close contact between the heat transfer tubes and the fin. Further, there is known a heat exchanger in which cut-and-raised portions called slits or louvers are formed that are open toward a direction in which air mainly flows, or a heat exchanger in which protruding portions called scratches or waffles are formed that protrude against a direction in which air mainly flows. In these heat exchangers, the surface area in which heat is exchanged is increased by the cut-and-raised portions or the protruding portions, thereby improving heat exchange performance. Moreover, there is known, for example, a heat exchanger in which a plurality of passages are formed inside a heat transfer tube, or a heat exchanger in which grooves are formed in the inner surface of a heat transfer tube. In these heat exchangers as well, the surface area in which heat is exchanged is increased by the plurality of passages or the grooves, thereby improving heat exchange performance.
Note that, when the heat exchanger operates as an evaporator, moisture in the air adheres to the heat exchanger as condensed water. In the heat exchanger, a drainage region where water adhering to the fin is drained is formed on the fin at a part other than the cutout portions. Further, the condensed water on the heat exchanger passes along the drainage region and is drained to the lower side of the fin. In this case, a water droplet adhering to a part above the cutout portion of the fin falls onto the upper surface of the heat transfer tube inserted into the cutout portion due to the gravity. Then, the water droplet runs around the end of the heat transfer tube to reach the lower surface of the heat transfer tube. Then, the water droplet falls onto the upper surface of the heat transfer tube provided on the lower side. In contrast, a water droplet adhering to the drainage region of the fin continues to descend while maintaining a constant speed because there is no obstacle such as the heat transfer tube on the lower side. That is, the descent of the water droplet adhering to a part above the cutout portion is hindered by the obstacle that is the heat transfer tube compared with the water droplet adhering to the drainage region. As a result, it takes a long period of time to reach the lower end of the heat exchanger.
Further, when the heat exchanger is mounted in an outdoor unit and operates as an evaporator, frost is formed from moisture in the air and adheres to the heat exchanger. Air-conditioning apparatuses, refrigerating apparatuses, or other apparatuses including a heat exchanger perform a defrosting operation to melt frost adhering to the heat exchanger. The frost is melted into a water droplet and the water droplet passes along the drainage region and is drained to the lower side of the fin similarly to the condensed water. Note that, when a water droplet remains above the cutout portion even after the defrosting operation is finished and a heating operation is started, the water droplet becomes frozen and grows again. Consequently, the reliability is decreased due to damage to the heat transfer tube or other cause. Further, the space around the heat transfer tube is closed by the frost, thereby influencing an increase in airflow resistance and a decrease in resistance to frost formation. Further, during the defrosting operation, it is necessary to melt the frozen water droplet as well as the frost adhering to the heat exchanger when the heat exchanger operates as an evaporator. Consequently, the comfort level is decreased due to an increase in defrosting time and the average heating capacity in a predetermined period of time is decreased due to repetition of the heating operation and the defrosting operation.
Patent Literature 1 discloses a heat exchanger in which louvers are provided between cutout portions of a fin and protruding portions are provided in a drainage region. Further, Patent Literature 2 discloses a heat exchanger in which protruding portions are provided in a drainage region. Patent Literature 2 discloses a sectorial protruding portion formed to cover the end of the cutout portion of the fin, and a linear protruding portion extending up to the other side portion of the fin.